IPv6 & MAC Addresses

Discussion in 'Apple, Inc and Tech Industry' started by guzhogi, May 11, 2007.

  1. guzhogi macrumors 68030


    Aug 31, 2003
    Wherever my feet take me…
    Just thinking about how IPv6 uses 128 bits to identify a host & network, while a MAC address is only 48 bits. Wouldn't it make sense to just use the MAC address as the host portion of an IP address? Then the 80 other bits can be used for network. Maybe the first 8 bits for country, then some for state/province, then county, then city. I know some organizations have multinational so maybe something different.
  2. djdawson macrumors member


    Apr 28, 2005
    You could do that...

    ...but the notion of using MAC addresses for higher layer addressing pretty died years ago (I know DECnet used MAC addresses, and I think Token Ring did, too). Because you might swap hardware in a machine, or swap machines, tying a MAC address to an individual host is less of a good idea than it initially seems, and it's generally better to de-couple Layer 2 addressing from the higher layers and let ARP deal with the necessary association. The typical way IPv6 addresses are used is to imbed your old IPv4 address in the lower order part of the address (assuming there's an existing IPv4 infrastructure), put a locally administered subnet around that (if needed), and the higher layers of network subnetting above that.

    Does that seem reasonable?
  3. EricNau Moderator emeritus


    Apr 27, 2005
    San Francisco, CA
    As djdawson already pointed out, MAC addresses can be traced to exactly one piece of hardware worldwide, and thus it's user as well. By separating the IP address from the MAC address, you're keeping the same anonymity that IPv4 has.
  4. yg17 macrumors G5


    Aug 1, 2004
    St. Louis, MO
    Yep, wouldn't be a good idea. Simple example:

    You have a server out there on the internet. So I don't have to type out a long IPv6 address or MAC address, lets say the network number is 1.2.3 and the MAC is 4.5.6. Using your example of using the MAC for the host part of the IP, we'd get an IP of (yes, I know this IP is completely invalid. Same with the MAC), correct? You got your DNS for your domain pointing there, and who knows what else.

    Now, that server's NIC card dies. You put in a new NIC, but it's MAC is 7.8.9. So now, that machine's IP becomes Which means your DNS is invalid and needs updating, and anything else you have pointing to that IP breaks. Just adds a lot of extra work to what would've been a 5 minute NIC swap.

    In general, MACs should only matter within the subnet. When 2 hosts are communicating over a network, if the 2 of them are in different subnets, they shouldn't be concerned with the other's MAC. That subnet's router takes care of the MAC stuff

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